Asymmetrical Concrete Backerboard

ABSTRACT

The present invention is a backerboard having a fiberglass mesh on one side, and a impervious reinforcement membrane on the other side. The backerboard incorporates a low density, high compressive strength concrete core having an upper principal surface and a lower principal surface. The upper principal surface of the core is covered by a fiberglass mesh reinforcement layer, itself covered and bonded to the core by a thin layer of Portland cement. The lower principal surface of the backerboard is covered with a high tensile strength, impervious reinforcement membrane.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a continuation of application Ser. No. 12/710,109, filed 22 Feb. 2010, now U.S. Pat. No. 8,413,333, which application is a divisional of application Ser. No. 09/829,256, filed 9 Apr. 2001, each of which are hereby incorporated in their entirety as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to a composite structural panel, and more particularly to an asymmetrical concrete backerboard having a cementitious bonding surface on one side, and an impervious reinforcement membrane on the opposite side of the board.

2. Description of Related Art

The conventional backerboard is made up of a rectangular panel of solid concrete, the concrete core, having both major surfaces covered with fiberglass mesh. The fiberglass mesh adds flexural strength to the board, and provides no resistance to water penetration through the board. Concrete backerboards are used extensively in the construction of interior and exterior floors, walls and ceilings. The concrete backerboard is a superior substrate or underlayment for stucco, ceramic tile, marble, and other tile-like surfaces located in wet areas, such as shower walls and bathtub surrounds, and building exterior walls.

Typically, the concrete core of the backerboard is a low density, high compressive strength, concrete core. The fiberglass mesh reinforcement layers overlay both major faces of the core, with each of these pervious fiberglass layers themselves covered with a thin layer of Portland cement. Backerboards have textured cementitious surfaces that provide for a high strength bond with mastics and Portland cement mortars that are used to adhere tile to the substrate in wet areas.

While the conventional backerboard is generally stable and water resistant, it is not an ideal construction panel for use in wet environments due to several inherent limitations. For example, it is generally recommended by backerboard manufactures, and required by most building codes, to use an additional impervious moisture barrier behind the backerboard. Thus, contractors are forced to install the backerboard and separate moisture barrier in the field, at the construction site. Use of an impervious barrier membrane with the backerboard provides protection for the wood or steel structures under or behind the backerboard, and contains the moisture in the wet area. Examples of commonly used moisture barriers are felt paper, Tyvek®, spunbonded olefin and polyethylene.

An exemplary patent in this field includes U.S. Pat. No. 3,284,980 to Dinkel disclosing a precast panel of cement and aggregate reinforced with a skin membrane of fibrous material. Backerboard manufacturing techniques include a lightweight aggregate core faced on each side or face with a fiberglass mesh material bathed in a slurry of neat cement and pressed against the aggregate core, such that when the neat cement and the aggregate core are cured, there is provided a composite, fiberglass mesh reinforced, cementitious panel. U.S. Reissue Patent No. Re32,037 to Clear is a method for manufacturing cementitious reinforced panels and illustrates a concrete panel 11 having reinforcement layers 12, 13 and a polyethylene layer 20 adjacent one of the layers 12, 13. Layers 12 and 13 are described as mesh reinforcing elements, preferably constituting fiber mesh like pervious webs, each entrained in hydraulic cement. Layer 20 is a carrier sheet placed under reinforcing element 12 during manufacture.

Similarly U.S. Pat. No. 6,187,409 to Mathieu discloses a cementitious panel with reinforced edges and illustrates a concrete panel manufactured on a polyethylene film layer 2.

The protective film layer 2 must be used to protect conveyor belt layer 1 from the cementitious layer 4 on the lower surface of the panel during manufacture. The protective film layer 2 does not remain part of the cementitious panel after manufacture.

Mathieu discloses that the membrane 2 is not part of the final construction element or panel, but (just like Clear), this membrane 2 is only a temporary film membrane that protects the cementitious lower surface of the panel from the conveyor belt or support structure during the manufacturing process. This temporary film membrane is typically referred to in the art as a carrier sheet or carrier web. It is an object of the present invention to rid this requirement of the prior art use of a carrier web:

In addition to membrane 2, Mathieu also discloses a symmetric panel, with the consistent use of reinforcing mesh 3 on both the lower and upper principal surfaces of the symmetric panel.

U.S. Pat. No. 6,171,680 to Fahmy pertains to a paperboard composite sheathing. Due to their low strength, because they lack reinforcement layers and a high compressive strength cementitious core, paperboard sheathing materials cannot be used as a substrate to support heavy tile materials and the like (what concrete backerboards are used for), which is understood by those of skill in the construction art.

Yet, such methods of constructing backerboards are not only deficient because they produce an inferior wet-area panel, but also because they require the use of a carrier sheet or protective film.

It is evident from the prior art that an improved backerboard and method of constructing such an improved backerboard is needed. It can be seen that there is a need for a backerboard having at least one waterproof surface that can be delivered ready-made to the construction site, and a method for producing such a backerboard without resort to a carrier sheet or protective film.

BRIEF SUMMARY OF THE INVENTION

Briefly described, in a preferred form, the present invention is a backerboard having a fiberglass mesh on one side, and an impervious moisture barrier membrane on the other side. Such an asymmetrical backerboard design (the two major surfaces of the core having differing moisture-resistant layers, providing different moisture-resistant properties) incorporates numerous advantages over the conventional backerboard design, including having lower manufacture costs, having a waterproof panel deliverable on-site, and having a simplified manufacturing process by eliminating the use of a carrier sheet or web.

The present asymmetrical backerboard comprises a low density, high compressive strength concrete core having an upper principal surface and a lower principal surface. The upper principal surface of the core is covered by a fiberglass mesh reinforcement layer, itself covered and bonded to the core by a thin layer of Portland cement. Alternatively, if the core itself comprises a sufficient amount of randomly dispersed fiberglass fibers, the addition of the fiberglass mesh reinforcement layer may not be required. The lower principal surface of the backerboard is covered with a high tensile strength, impervious moisture barrier membrane.

The present backerboard construction eliminates the prior art necessity of the on-the-construction-site application of a moisture barrier behind the backerboard. It exhibits all of the structural, bonding and workability properties of conventional backerboards, and provides advanced water resistance.

The present method of constructing the backerboard dispenses with the prior art requirement of a carrier sheet or protective film. In a preferred embodiment of the invention, the panel is manufactured by the concurrent steps of running a continuous pervious reinforcement web through a web coating bath and then removing excess bath therefrom, and running a continuous impervious reinforcement web through a set of pinch rollers and atop a conveyor belt.

Core material is dispensed upon the impervious web via a hopper, and the combination of impervious web and core material run through a screed. The core material is then compacted. The bathed pervious web is then fed onto the top of the core material, forming a sandwich of, from bottom to top, impervious web, core material and pervious web. The composite is then cut into panels.

In an exemplary embodiment, the present invention is a prefabricated asymmetrical construction element comprising a cementitious core including alkaline resistant fibers and having an upper principal face and a lower principal face, an impervious non-cementitious reinforcement web disposed directly on the lower principal face of the core while the core is in a plastic state, the impervious reinforcement web remaining on the lower principal face of the core after the manufacture of the construction element, a cementitious bonding surface remaining on the upper principal face of the construction element after the manufacture of the construction element, and a non-cementitious surface remaining on the lower principal face of the construction element after the manufacture of the construction element, and the construction element being prefabricated by running a continuous web of impervious non-cementitious reinforcement membrane directly onto a conveyor belt, depositing a cementitious substance directly onto the impervious non-cementitious reinforcement membrane, and removing the construction element from the conveyor belt.

The alkaline resistant fibers can being chopped reinforcement fibers randomly dispersed in the core.

The impervious reinforcement web can comprise a reinforced polymer membrane.

The impervious reinforcement web can comprise water impervious paperboard.

The impervious reinforcement web can comprise spunbonded olefin.

The impervious reinforcement web can comprise an alkaline resistant dense polymer fiber mat.

The core can comprise Portland cement, alkaline resistant fibers, and one or more additives selected from the group consisting of expanded shale, expanded clay, sintered clay, pumice, slag, calcium carbonate, slate, diatomaceous earth, perlite, vermiculite, scoria, volcanic cinders, tuff, diatomite, sintered fly ash, industrial cinders, gypsum, foam beads and/or glass beads.

In an exemplary embodiment, the present invention is a prefabricated asymmetrical construction element comprising a cementitious core having an upper principal face and a lower principal face, the upper principal face having a single layer of pervious reinforcing mesh embedded in or adhered to the upper principal surface, an upper cementitious coating disposed on the upper principal face of the core and the pervious reinforcing mesh, an impervious non-cementitious reinforcement web disposed directly on the lower principal face of the core while the core is in a plastic state, the impervious reinforcement web remaining on the lower principal face of the core after the manufacture of the construction element, a cementitious bonding surface remaining on the upper principal face of the construction element after the manufacture of the construction element, and a non-cementitious surface remaining on the lower principal face of the construction element after the manufacture of the construction element, the construction element being prefabricated by running a continuous web of impervious non-cementitious reinforcement membrane directly onto a conveyor belt, depositing a cementitious substance directly onto the impervious non-cementitious reinforcement membrane, placing a layer of pervious non-cementitious reinforcement material only atop the cementitious substance, and removing the construction element from the conveyor belt.

The pervious reinforcement web can comprise a polymer coated scrim or woven mesh of alkaline resistant fiberglass.

The impervious reinforcement web can comprise a reinforced polymer membrane.

The impervious reinforcement web can comprise water impervious paperboard.

The impervious reinforcement web can comprise spunbonded olefin.

The impervious reinforcement web can comprise an alkaline resistant dense polymer fiber mat.

The core can comprise Portland cement, alkaline resistant fibers, and one or more additives selected from the group consisting of expanded shale, expanded clay, sintered clay, pumice, slag, calcium carbonate, slate, diatomaceous earth, perlite, vermiculite, scoria, volcanic cinders, tuff, diatomite, sintered fly ash, industrial cinders, gypsum, foam beads and/or glass beads.

In an exemplary embodiment, the present invention is a prefabricated asymmetrical construction element comprising a cementitious core including alkaline resistant fibers and having an upper principal face and a lower principal face, an impervious non-cementitious reinforcement web disposed directly on the lower principal face of the core, a cementitious bonding surface on the upper principal face of the construction element, and a non-cementitious surface on the lower principal face of the construction element.

The alkaline resistant fibers can comprise chopped reinforcement fibers randomly dispersed in the core, and the impervious non-cementitious reinforcement web can comprise a reinforced polymer membrane, water impervious paperboard, spunbonded olefin, and/or an alkaline resistant dense polymer fiber mat.

The core can comprise Portland cement, alkaline resistant fibers, and one or more additives selected from the group consisting of expanded shale, expanded clay, sintered clay, pumice, slag, calcium carbonate, slate, diatomaceous earth, perlite, vermiculite, scoria, volcanic cinders, tuff, diatomite, sintered fly ash, industrial cinders, gypsum, foam beads and/or glass beads.

In an exemplary embodiment, the present invention is a prefabricated asymmetrical construction element comprising a cementitious core having an upper principal face and a lower principal face, the upper principal face having a single layer of pervious reinforcing mesh embedded in or adhered to the upper principal surface, an upper cementitious coating disposed on the upper principal face of the core and the pervious reinforcing mesh, an impervious non-cementitious reinforcement web disposed directly on the lower principal face of the core, a cementitious bonding surface on the upper principal face of the construction element, and a non-cementitious surface on the lower principal face of the construction element.

In an exemplary embodiment, the present invention is a prefabricated asymmetrical construction element prepared by a process, wherein the prefabricated asymmetrical construction element comprises a cementitious core including alkaline resistant fibers and having an upper principal face and a lower principal face, an impervious non-cementitious reinforcement web disposed directly on the lower principal face of the core, a cementitious bonding surface on the upper principal face of the construction element, and a non-cementitious surface on the lower principal face of the construction element, wherein the process comprises running a continuous web of the impervious non-cementitious reinforcement web, and depositing the core onto the impervious non-cementitious reinforcement web while the core is in a plastic state, the impervious reinforcement web remaining on the lower principal face of the core after the manufacture of the construction element.

The process can further comprise placing a layer of pervious non-cementitious reinforcement material on the cementitious bonding surface.

The process can further comprise running the continuous web of the impervious non-cementitious reinforcement web directly onto a conveyor belt.

The process can further comprise curing the core.

The process can further comprise permanently adhering the web of impervious non-cementitious reinforcement web directly to the cementitious core during curing of the core, the continuous web of impervious non-cementitious reinforcement web forming the non-cementitious surface on the lower principal face of the construction element as the construction element is removed from the conveyor belt

The core can be the first material or element placed on the web of impervious non-cementitious reinforcement web, and wherein the web of impervious non-cementitious reinforcement web is not a carrier sheet for the core, but is permanently attached to the core to form the lower principal face of the construction element.

The process can further comprise cutting the construction element into panels.

In an exemplary embodiment, the present invention is a method of manufacturing a construction element for use as an underlayment or backerboard, the method comprising running a continuous web of impervious reinforcement membrane directly onto a conveyor belt, depositing a cementitious core material onto the web of impervious reinforcement membrane, disposing a reinforcement mesh onto the top surface of the cementitious core material, curing the core material, permanently adhering the web of impervious reinforcement membrane directly to the cementitious core material during the curing of the core material, the continuous web of impervious reinforcement membrane forming a bottom impervious non-cementitious surface of the construction element as the construction element is removed from the conveyor belt, and permanently adhering the reinforcement mesh to the top surface of the cementitious core material during the curing of the core material, the reinforcement mesh forming a top pervious cementitious surface of the construction element.

The core material can be the first material or element placed on the web of impervious reinforcement membrane, wherein the reinforcement mesh is embedded into the core material, and the web of impervious reinforcement membrane is not a carrier sheet for the core material, but is permanently attached to the core material to form the bottom impervious non-cementitious surface of the construction element.

The method can further comprise running the continuous web of the impervious reinforcement membrane from a roll through a pinch roller assembly.

The method can further comprise screeding the core material to provide a flat and level evenly distributed layer of core material after depositing on the web of impervious reinforcement membrane.

The method can further comprise conveying the reinforcement mesh through a bath of coating material.

The method can further comprise compacting the cementitious core material on the web of impervious reinforcement membrane to enhance bonding between the cementitious core material and impervious reinforcement membrane such that the impervious membrane is permanently attached to the core material.

The method can further comprise urging the reinforcement mesh on to the top surface of the core material by conveying the reinforcement mesh and core material underneath a drag bar.

The method can further comprise cutting the construction element into panels and stacking the panels to cure, such that after curing a bottom surface of a finished panel does not have a reinforcement mesh embedded therein.

In an exemplary embodiment, the present invention is a method of making a construction element, the method consisting essentially of running a continuous web of impervious non-cementitious reinforcement membrane directly onto a conveyor belt, depositing a cementitious substance directly onto the impervious non-cementitious reinforcement membrane, placing a layer of pervious non-cementitious reinforcement material only atop the cementitious substance, and removing the construction element from the conveyor belt.

In an exemplary embodiment, the present invention is a construction element for use as an underlayment or backerboard comprising a core having an upper principal surface and a lower principal surface, and an impervious membrane on the lower principal surface of the core, the core including alkaline resistant fibers.

In an exemplary embodiment, the present invention is a construction element for use as an underlayment or backerboard comprising a core having an upper principal surface and a lower principal surface, a pervious upper reinforcement material on the upper principal surface of the core, an upper coating in communication with the upper principal surface of the core and the pervious upper reinforcement material, and an impervious membrane on the lower principal surface of the core.

In an exemplary embodiment, the present invention is a construction element for use as an underlayment or backerboard comprising a cement core having an upper principal surface and a lower principal surface, a pervious reinforcement layer on the upper principal surface of the core, a cement slurry binding the reinforcement layer to the upper principal surface of the core, and a high tensile strength, impervious moisture barrier membrane bound to the lower principal surface of the core.

In an exemplary embodiment, the present invention is a method of manufacturing a construction element for use as an underlayment or backerboard comprising conveying a sheet of impervious reinforced membrane through a core station, and depositing at the core station a core material on the impervious reinforced membrane, the core material including alkaline resistant fibers, and the impervious reinforced membrane acting as a carrier sheet.

In an exemplary embodiment, the present invention is a method of manufacturing a construction element for use as an underlayment or backerboard comprising conveying a sheet of impervious reinforced membrane through a core station, depositing at the core station a core material on the impervious reinforced membrane, and layering a pervious membrane atop the core material such that the core material is sandwiched between the pervious membrane and the impervious membrane, the impervious reinforced membrane acting as a carrier sheet throughout the manufacturing process.

In an exemplary embodiment, the present invention is a method of manufacturing a construction element for use as an underlayment or backerboard comprising the following steps conveying a sheet of impervious reinforced membrane through the steps of the method of manufacturing, depositing a core material from a core material hopper to the conveyed impervious reinforced membrane, screeding the core material on the conveyed sheet of impervious reinforced membrane with a screed, compacting the core material on the conveyed sheet of impervious reinforced membrane with a compactor, bathing a conveyed pervious reinforced membrane through a bath of cement, layering the pervious reinforced membrane on the core material on the conveyed sheet of impervious reinforced membrane; and cutting the manufactured construction element into panels.

It is thus an object of the present invention to provide an asymmetrical backerboard and a method for making such a board.

Further, it is an object of the present invention to provide a construction panel having at least one major surface which is highly resistant to the penetration of water.

These and other objects, features, and advantages of the present invention will become more apparent upon reading the following specification in conjunction with the accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front sectional view of a prior art backboard.

FIG. 2 is a side view of FIG. 1.

FIG. 3 is a front sectional view of the present asymmetrical backboard according to a preferred embodiment of the present invention.

FIG. 4 is a side view of FIG. 3.

FIG. 5 is a block diagram of a preferred construction method for the backerboard of FIG. 3.

FIG. 6 illustrates the manufacture of the backerboard of FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The components of the present invention are referenced herein as follows:

NO. COMPONENT 10 Prior Art Backerboard 12 Concrete Core 14 Fiberglass Mesh Reinforcement 16 Layer of Portland Cement 20 Present Asymmetrical Backerboard 22 Concrete Core 24 Upper Principal Surface of Core 26 Lower Principal Surface of Core 28 Upper Reinforcement Material 32 Upper Coating 34 Impervious Membrane 40 Present Manufacturing Process 42 Roll of Impervious Membrane 44 Pinch Roller Assembly 46 Conveyor Belt 48 Core Feed Hopper 52 Screed 54 Compaction Station 56 Compaction Roll 58 Bath 62 Roller Assembly 64 Doctor Assembly 66 Drag Bar 72 Step of Feeding 74 Step of Depositing 76 Step of Screeding 78 Step of Compacting 82 Step of Bathing 84 Step of Layering 86 Step of Cutting

To facilitate an understanding of the principles and features of the various embodiments of the invention, various illustrative embodiments are explained below. Although exemplary embodiments of the invention are explained in detail, it is to be understood that other embodiments are contemplated. Accordingly, it is not intended that the invention is limited in its scope to the details of construction and arrangement of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or carried out in various ways. Also, in describing the exemplary embodiments, specific terminology will be resorted to for the sake of clarity.

It must also be noted that, as used in the specification and the appended claims, the singular forms “a,” “an” and “the” include plural references unless the context clearly dictates otherwise. For example, reference to a component is intended also to include composition of a plurality of components. References to a composition containing “a” constituent is intended to include other constituents in addition to the one named.

Also, in describing the exemplary embodiments, terminology will be resorted to for the sake of clarity. It is intended that each term contemplates its broadest meaning as understood by those skilled in the art and includes all technical equivalents which operate in a similar manner to accomplish a similar purpose.

Ranges may be expressed herein as from “about” or “approximately” or “substantially” one particular value and/or to “about” or “approximately” or “substantially” another particular value. When such a range is expressed, other exemplary embodiments include from the one particular value and/or to the other particular value.

Similarly, as used herein, “substantially free” of something, or “substantially pure”, and like characterizations, can include both being “at least substantially free” of something, or “at least substantially pure”, and being “completely free” of something, or “completely pure”.

By “comprising” or “containing” or “including” is meant that at least the named compound, element, particle, or method step is present in the composition or article or method, but does not exclude the presence of other compounds, materials, particles, method steps, even if the other such compounds, material, particles, method steps have the same function as what is named.

It is also to be understood that the mention of one or more method steps does not preclude the presence of additional method steps or intervening method steps between those steps expressly identified. Similarly, it is also to be understood that the mention of one or more components in a composition does not preclude the presence of additional components than those expressly identified.

The materials described as making up the various elements of the invention are intended to be illustrative and not restrictive. Many suitable materials that would perform the same or a similar function as the materials described herein are intended to be embraced within the scope of the invention. Such other materials not described herein can include, but are not limited to, for example, materials that are developed after the time of the development of the invention.

It should be noted that as used herein the term “pervious” defines a property of a material, that property enabling free water to penetrate through a material, and that the term “impervious” defines a property of a material, that property being highly resistant against enabling free water to penetrate through a material. An impervious material may enable water vapor to penetrate through a material.

Referring now in detail to the drawing figures, wherein like reference numerals represent like parts throughout the several views, FIGS. 1 and 2 illustrate a conventional backerboard 10 comprising a low density, high compressive strength, concrete core 12. A layer of fiberglass mesh reinforcement 14 covers both major faces of the core 12, with each of these pervious fiberglass layers themselves 14 covered with a thin layer 16 of Portland cement.

As shown in FIGS. 3 and 4, The present invention 20 comprises a core 22 having an upper principal surface 24 and a lower principal surface 26, an upper reinforcement material 28 in contact with the upper principal surface 24 of the core 22, an upper coating 32 in communication with the upper principal surface 24 of the core 22 and the upper reinforcement material 28, and an impervious membrane 34 covering the lower principal surface 26 of the core 22.

The core 22 can comprise low, medium and high slump concrete. The concrete preferably includes Portland cement and lightweight fillers and/or aggregates of, for example, expanded shale, expanded clay, sintered clay, pumice, slag, calcium carbonate, slate, diatomaceous slate, perlite, vermiculite, scoria, volcanic cinders, tuff, diatomite, sintered fly ash, industrial cinders, gypsum, foam beads, glass beads and the like. Other additives that can be mixed with the Portland cement include lightweight sand and alkaline resistant fibers such as chopped reinforcement fibers, randomly dispersed in the core 22.

The upper reinforcement material 28 is preferably pervious and comprises woven fiberglass mesh or fiberglass skrim with an alkaline resistant coating. Alternatively, the reinforcement material 28 can be a polymer fiber mat. In yet another embodiment, the upper reinforcement material 28 can, in essence, be made a part of the core 22, such that the addition of a separate layer of upper reinforcement material is not necessary. For example, the core 22 can comprise a sufficient amount of alkaline resistant fibers wherein an upper reinforcement material layer need not be an additional element of the present backerboard 10.

The upper coating 32 can be a Portland cement slurry being either neat or foamed. The slurry can comprise fine aggregate and/or filler material.

The impervious membrane 34 preferably comprises a polymer membrane, for example, a fiber mat, Tyvek®, Typar®, brand spunbonded olefin, or a layer of waterproofed paper or cardboard. The impervious membrane 34 can specifically include an alkaline resistant dense polymer fiber mat.

Manufacture

The present manufacturing process 40 (as shown left to right in FIGS. 5 and 6) incorporates a first feeding step 72 of running a continuous roll 42 of the impervious membrane 34 out through a pinch roller assembly 44. The impervious membrane 34 is at that point supported and conveyed by a conveyor belt 46.

In a second depositing step 74, the membrane 34 is conveyed beneath a core material dispense hopper 48, through which the cementitious core mix of the core 22 if fed onto the membrane 34. Hopper 48 can include elements (not shown), for example, a metering gate for controlling the amount of mix laid onto the membrane 34.

A third screeding step 76 of the present manufacturing process includes reducing the thickness of the core mix. The conveyor belt 46 carries the membrane 34/core mix composite through screed 52 to reduce the thickness, and smooth out the upper surface, of the core mix. Thereafter, in a fourth compacting step 78, the conveyor belt 46 moves the membrane 34/core mix composite into a compaction station 54 that can include a compaction roll 56 that which serves to compact the core mix against the impervious membrane 34. This compaction increases the density of the core and enhances the bond of the membrane 34 to the core mix.

In a fifth bathing step 82, a roll of the upper reinforcement material 28 is run through a bath 58 of the upper coating 32, and in a sixth layering step 84, the upper reinforcement material 28 is laid down on the core mix. A roller assembly 62 can serve to draw the upper reinforcement material 28 through the bath 58 and a doctor assembly 64 can remove any excessive slurry from the material 28. A drag bar 66 can be positioned above the material 28 which drags against its upper surface, thereby serving to urge core mix on the upper surface of the material 28 into the interstices of the material 28 and through the material 28. In a final cutting step 86, the backerboard is then cut downstream (not shown) into panels.

The present manufacturing process 40 has great advantages over the prior art processes. During the manufacture of the standard concrete backerboard, with cementitious surfaces on both sides, the conventional forming conveyor must be protected from contact with the bottom of the core/pervious (as opposed to the present invention's impervious membrane 34) surface while in its plastic state. This is accomplished by the use of a form, a carrier sheet or a disposable protective film. These forms and carrier sheets are treated with a release agent and remain with the backerboard until it has hardened, at which time the form or carrier sheet is separated from the backerboard, cleaned and recoated with release agent to be reentered into the forming operation. In the case of manufacturing with a protective film, which is dispensed onto the forming conveyer where the backerboard is formed on the protective film. This film remains with the backerboard until it hardens at which time the protective film is removed and disposed.

The present invention avoids the carrier sheet problem by providing a backerboard with a cementitious surface on only one side, and a high tensile strength impervious membrane 34 on the other side. Manufacturing this improved backerboard with the membrane 34 on the bottom side eliminates the need for a form, a carrier sheet, a release agent or a protective film. The impervious membrane 34 which is incorporated into the present backerboard composite, essentially becomes a non-disposable carrier web. The manufacturing process thus is greatly simplified by ridding the process and equipment required to treat the carrier or form with release agent, dispensing the carrier, form, or film into the forming process, separating the carrier, form, or film from the backerboard, cleaning the carrier or form, retreating the carrier or form with release agent, and/or dispensing of and disposing of the protective film. Additionally the cost of the impervious high tensile strength membrane 34 is less costly than vinyl coated fiberglass mesh with comparable tensile strength.

Additionally, the use of randomly dispersed chopped fibers in the core is novel and no-obvious in the art of manufacturing concrete backerboard panels. Although the use of random reinforcement fibers has been commonly used with thick voluminous poured concrete structures, the use of random reinforcement fibers in conventional symmetric concrete backerboard panels is not known.

For example, neither Mathieu nor Dinkel (discussed previously) require additional tensile reinforcement due to the use of a fiberglass mesh, or skrim, on both the upper and lower principal surfaces of the conventional symmetric backerboard panel. This pervious fiberglass mesh or skrim is an inherently high tensile strength material. Using randomly dispersed reinforcement fibers in the core material allows the option to use a standard weight impervious membrane, which has significantly less tensile strength than fiberglass mesh or skrim, on the lower surface of the present asymmetrical backerboard panel.

Additionally, the present use of a membrane being a reinforced polymer membrane is novel and no-obvious in the art of manufacturing concrete backerboard panels. Although the impervious materials, reinforced polymer membrane, spunbonded olefin, alkaline resistant dense polymer fiber mat, or waterproof paperboard, have existed for many years, the use of these materials to reinforce symmetrical backerboard panels is not known.

For example, Dinkel and Mathieu disclose the use of the same reinforcing mesh on both the upper and lower principal surfaces forming a conventional symmetrically reinforced panel. The present asymmetrical backerboard in an exemplary embodiment has different reinforcing materials, a pervious mesh on the upper principal surface and an impervious reinforcing membrane on the lower principal surface.

The present invention is patentably distinct from Fahmy (discussed previously) in numerous ways, among them: Fahmy teaches only the use of a liquid resin applied to the sheathing to become the “impervious membrane”, although the present invention cannot utilize liquid-applied impervious membranes; ultimately, the Fahmy “impervious membrane” comprises at least three separate layers of materials bonded to the core, wherein the present inventions impervious membrane can be a single layer; and Fahmy requires an impervious membrane on both principal surfaces of the sheathing, while the present invention can have only one.

It can be appreciated by those of skill in the art that the Fahmy liquid resin coatings must first be applied to a web before adhering to the core. Yet, in an exemplary embodiment, the impervious membrane of the present invention is not, and cannot, be a layer of liquid resin on its lower surface. This would cause the liquid resin to adhere to the conveyor belt or form on which the baker board is manufactured. The present invention comprises a method of constructing the backer board that dispenses with the prior art requirement of a carrier sheet or web. Thus, the benefit of manufacturing the present backer board without a carrier sheet or web would be lost if a liquid resin vapor barrier were used as an impervious membrane on the present invention.

Also when exposed to moisture change, Fahmy's unstable paperboard core would expand and contract on the magnitude of five to ten times that of the tile-like materials bonded to the paperboard sheathing, which would cause the tile like materials to shear away from the sheathing in just a few wet/dry cycles. On the other hand, when exposed to moisture change, concrete backerboards, with their stable cementitious core, expand and contract at a rate very close to that of the tile like materials, making these backerboards historically superior substrates for tile materials and the like.

Further, an exemplary embodiment of the present invention comprises a cement core, with one or more reinforcement layers bonded to the major surfaces. Fahmy neither teaches nor suggests a cement core, or a reinforcement layer, and to alter the teachings of Fahmy to include the cement core and/or reinforcement layers of, for example, Mathieu, would change the very essence of the paperboard sheathing of Fahmy.

Further, the permeable layer of Fahmy is significantly different than the impervious membrane of the present invention. Fahmy teaches that to construct the membrane with liquid water impermeability and water vapor permeability requires three separate layers of materials bonded to the core 12. These materials include a permeable resin (16 or 22), a paperboard layer (14 or 20), and an adhesive layer (18 or 24) with a plurality of apertures 26. The paperboard layer (14 or 20) must be used to separate the resin layer (16 or 22) from the special adhesive layer (18 or 24) with a plurality of apertures. If the paperboard layer (14 or 20) is not used, then the resin (16 or 22) would fill in the apertures 26 in the adhesive layer (18 or 24), thus rendering the membrane vapor impermeable.

On the other hand, a preferred embodiment of the present invention has only one layer of web material to create the impervious membrane.

Further, Fahmy teaches that two layers of impervious membranes (16, 14, 18) and (22, 20, 24) must be used, one on each side of the core 12, in order to construct a composite sheathing with liquid water impermeability and water vapor permeability. A preferred embodiment of the present invention has only one layer of impervious membrane adhered directly to the bottom surface of the core.

Additionally, Fahmy only teaches that in order to adhere the outer layers of paperboard to the core while allowing the composite to remain vapor permeable, a layer of adhesive with a plurality of apertures must be printed on the outer layers of paperboard with a special engraved transfer roll. An exemplary embodiment of the present invention does not require this special adhesive with apertures, thus illuminating the need for a special engraved transfer roll in the manufacturing process. In some embodiments, the present invention requires no adhesive at all due to the adhesive nature of the plastic cementitious core material that is cast onto the impervious membrane during manufacturing. After the core cures, the impervious membrane remains adhered to the core. Fahmy teaches away from the invention by requiring this critical need for an adhesive layer with apertures therethrough.

Numerous characteristics and advantages have been set forth in the foregoing description, together with details of structure and function. While the invention has been disclosed in several forms, it will be apparent to those skilled in the art that many modifications, additions, and deletions, especially in matters of shape, size, and arrangement of parts, can be made therein without departing from the spirit and scope of the invention and its equivalents as set forth in the following claims.

Therefore, other modifications or embodiments as may be suggested by the teachings herein are particularly reserved as they fall within the breadth and scope of the claims here appended. 

What is claimed is:
 1. A prefabricated asymmetrical construction element comprising: a cementitious core including alkaline resistant fibers and having an upper principal face and a lower principal face; an impervious non-cementitious reinforcement web disposed directly on the lower principal face of the core; a cementitious bonding surface on the upper principal face of the construction element; and a non-cementitious surface on the lower principal face of the construction element.
 2. The construction element of claim 1, the alkaline resistant fibers comprising chopped reinforcement fibers randomly dispersed in the core.
 3. The construction element of claim 1, the impervious non-cementitious reinforcement web comprising a reinforced polymer membrane.
 4. The construction element of claim 1, the impervious non-cementitious reinforcement web comprising water impervious paperboard.
 5. The construction element of claim 1, the impervious non-cementitious reinforcement web comprising spunbonded olefin.
 6. The construction element of claim 1, the impervious non-cementitious reinforcement web comprising an alkaline resistant dense polymer fiber mat.
 7. The construction element of claim 1, the core comprising Portland cement, alkaline resistant fibers, and one or more additives selected from the group consisting of expanded shale, expanded clay, sintered clay, pumice, slag, calcium carbonate, slate, diatomaceous earth, perlite, vermiculite, scoria, volcanic cinders, tuff, diatomite, sintered fly ash, industrial cinders, gypsum, foam beads and/or glass beads.
 8. A prefabricated asymmetrical construction element comprising: a cementitious core having an upper principal face and a lower principal face, the upper principal face having a single layer of pervious reinforcing mesh embedded in or adhered to the upper principal surface; an upper cementitious coating disposed on the upper principal face of the core and the pervious reinforcing mesh; an impervious non-cementitious reinforcement web disposed directly on the lower principal face of the core; a cementitious bonding surface on the upper principal face of the construction element; and a non-cementitious surface on the lower principal face of the construction element.
 9. A prefabricated asymmetrical construction element prepared by a process, wherein the prefabricated asymmetrical construction element comprises: a cementitious core including alkaline resistant fibers and having an upper principal face and a lower principal face; an impervious non-cementitious reinforcement web disposed directly on the lower principal face of the core; a cementitious bonding surface on the upper principal face of the construction element; and a non-cementitious surface on the lower principal face of the construction element; wherein the process comprises: running a continuous web of the impervious non-cementitious reinforcement web; and depositing the core onto the impervious non-cementitious reinforcement web while the core is in a plastic state, the impervious reinforcement web remaining on the lower principal face of the core after the manufacture of the construction element.
 10. The prefabricated asymmetrical construction element prepared by the process of claim 9, the process further comprising placing a layer of pervious non-cementitious reinforcement material on the cementitious bonding surface.
 11. The prefabricated asymmetrical construction element prepared by the process of claim 9, the process further comprising running the continuous web of the impervious non-cementitious reinforcement web directly onto a conveyor belt.
 12. The prefabricated asymmetrical construction element prepared by the process of claim 9, the process further comprising curing the core.
 13. The prefabricated asymmetrical construction element prepared by the process of claim 12, the process further comprising permanently adhering the web of impervious non-cementitious reinforcement web directly to the cementitious core during curing of the core, the continuous web of impervious non-cementitious reinforcement web forming the non-cementitious surface on the lower principal face of the construction element as the construction element is removed from the conveyor belt
 14. The prefabricated asymmetrical construction element prepared by the process of claim 9, wherein the core is the first material or element placed on the web of impervious non-cementitious reinforcement web, and wherein the web of impervious non-cementitious reinforcement web is not a carrier sheet for the core, but is permanently attached to the core to form the lower principal face of the construction element.
 15. The prefabricated asymmetrical construction element prepared by the process of claim 9, the process further comprising cutting the construction element into panels. 